Laminate materials come in various types and have a wide variety of end uses. One area of laminate materials that has been very active is high-pressure decorative laminates or HPDLs. High pressure decorative laminates are used in such applications as countertops (hereinafter referred to as counters), desk tops, cabinets, wall paneling, furniture, etc. There are about seven different types of HPDLs; namely, general-purpose, post-forming, cabinet-liner, backer, specific-purpose, high-wear, and fire-rated. Each of these types of laminate materials are usually constructed out of a coating material such as a laminate, a substrate and some type of adhesive.
In the past, one of the most popular types of laminate materials has been paper based laminates such as Formica.RTM.. Typically, the substrate material for a Formica.RTM.-type product is also a wood based material such as particleboard. However, Formica.RTM. has a number of problems in that it is very brittle, susceptible to stress cracking, difficult to process, and difficult to repair. Consequently, Formica.RTM. is relatively limited in its application.
Thus, it would be desirable to use different types of coating materials which do not suffer from the drawbacks of paper based laminates such as Formica.RTM., and which allow for a wider variety of end-use applications. For example, it would be highly desirable to employ a thermoplastic material such as a polyester or even a thermosetting resin, depending on the particular application desired. By the same token, it would also be desirable to vary the substrate materials depending on the end-use application and the desired cost.
However, the present inventors discovered that one of the most difficult problems associated with employing polymer based coating materials with different types of substrates, e.g., cellulose based substrates or the like, is that the two materials usually have very different expansion properties. For example, the coefficient of thermal expansion between, e.g., a highly filled polyester resin and, e.g., particleboard, can be an order of magnitude or more different from one another. Because the different layers expand at substantially different rates and to significantly different degrees, the coating material and the substrate are particularly susceptible to separation one from another.
This problem is unique as compared to Formica.RTM., because Formica.RTM. and the wood based substrate to which it is adhered tend to have very similar expansion properties, i.e., expansion properties which are typically less than about 100%. Even then, the prior art teaches that such differences in expansion can and should be minimized by aligning the grains of the substrate and coating materials so that they are as closely aligned as possible. In this manner they will expand and contract along the same lines and to the same degree.
Accordingly, it is an object of the present invention to effectively adhere together a substrate and a coating material having significantly different expansion properties using a composite adhesive and a spline material which has expansion properties similar to the coating material.
It is also an object of the present invention to provide a composite article of manufacture with a substrate and a coating material adhered to one another using a spline material either between the coating and substrate materials or at a joint, bend or other inherently weak bond location in the coating material in such a manner that the coating and substrate materials do not separate even when expanding at significantly different rates.